Re: [ndctl PATCH v2] cxl/list: remove libtracefs build dependency for --media-errors

[Alison Schofield <alison.schofield@intel.com>]

On Wed, Sep 24, 2025 at 04:10:21PM -0700, Dan Williams wrote:
> Alison Schofield wrote:
> > When the --media-errors option was added to cxl list it inadvertently
> > changed the optional libtracefs requirement into a mandatory one.
> > Ndctl versions 80,81,82 no longer build without libtracefs.
> > 
> > Remove that dependency.
> > 
> > When libtracefs is disabled the user will see a 'Notice' level
> > message, like this:
> > 	$ cxl list -r region0 --media-errors --targets
> > 	cxl list: cmd_list: --media-errors support disabled at build time
> > 
> > ...followed by the region listing including the output for any other
> > valid command line options, like --targets in the example above.
> > 
> > When libtracefs is disabled the cxl-poison.sh unit test is omitted.
> > 
> > The man page gets a note:
> > 	The media-error option is only available with -Dlibtracefs=enabled.
> > 
> > Reported-by: Andreas Hasenack <andreas.hasenack@canonical.com>
> > Fixes: d7532bb049e0 ("cxl/list: add --media-errors option to cxl list")
> > Closes: https://github.com/pmem/ndctl/issues/289
> > Signed-off-by: Alison Schofield <alison.schofield@intel.com>
> > ---
> > 
> > Changes in v2:
> > - Notify and continue when --media-error info is unavailable (Dan)
> > 
> > 
> >  Documentation/cxl/cxl-list.txt |  2 ++
> >  config.h.meson                 |  2 +-
> >  cxl/json.c                     | 15 ++++++++++++++-
> >  cxl/list.c                     |  6 ++++++
> >  test/meson.build               |  9 +++++++--
> >  5 files changed, 30 insertions(+), 4 deletions(-)
> > 
> > diff --git a/Documentation/cxl/cxl-list.txt b/Documentation/cxl/cxl-list.txt
> > index 9a9911e7dd9b..0595638ee054 100644
> > --- a/Documentation/cxl/cxl-list.txt
> > +++ b/Documentation/cxl/cxl-list.txt
> > @@ -425,6 +425,8 @@ OPTIONS
> >  	"source:" is one of: External, Internal, Injected, Vendor Specific,
> >  	or Unknown, as defined in CXL Specification v3.1 Table 8-140.
> >  
> > +The media-errors option is only available with '-Dlibtracefs=enabled'.
> > +
> >  ----
> >  # cxl list -m mem9 --media-errors -u
> >  {
> > diff --git a/config.h.meson b/config.h.meson
> > index f75db3e6360f..e8539f8d04df 100644
> > --- a/config.h.meson
> > +++ b/config.h.meson
> > @@ -19,7 +19,7 @@
> >  /* ndctl test support */
> >  #mesondefine ENABLE_TEST
> >  
> > -/* cxl monitor support */
> > +/* cxl monitor and cxl list --media-errors support */
> >  #mesondefine ENABLE_LIBTRACEFS
> >  
> >  /* Define to 1 if big-endian-arch */
> > diff --git a/cxl/json.c b/cxl/json.c
> > index e65bd803b706..a75928bf43ed 100644
> > --- a/cxl/json.c
> > +++ b/cxl/json.c
> > @@ -9,12 +9,15 @@
> >  #include <json-c/json.h>
> >  #include <json-c/printbuf.h>
> >  #include <ccan/short_types/short_types.h>
> > +
> > +#ifdef ENABLE_LIBTRACEFS
> >  #include <tracefs.h>
> > +#include "../util/event_trace.h"
> > +#endif
> 
> Maybe this is my kernel taste leaking through, but I am allergic to
> ifdef in ".c" files. In this case you could move the include of
> tracefs.h into event_trace.h and then ifdef guard all the parts of
> event_trace.h that need tracefs.h.
> 
> >  
> >  #include "filter.h"
> >  #include "json.h"
> >  #include "../daxctl/json.h"
> > -#include "../util/event_trace.h"
> >  
> >  #define CXL_FW_VERSION_STR_LEN	16
> >  #define CXL_FW_MAX_SLOTS	4
> > @@ -575,6 +578,7 @@ err_jobj:
> >  	return NULL;
> >  }
> >  
> > +#ifdef ENABLE_LIBTRACEFS
> >  /* CXL Spec 3.1 Table 8-140 Media Error Record */
> >  #define CXL_POISON_SOURCE_MAX 7
> >  static const char *const poison_source[] = { "Unknown", "External", "Internal",
> > @@ -753,6 +757,15 @@ err_free:
> >  	tracefs_instance_free(inst);
> >  	return jpoison;
> >  }
> > +#else
> > +static struct json_object *
> > +util_cxl_poison_list_to_json(struct cxl_region *region,
> > +			     struct cxl_memdev *memdev,
> > +			     unsigned long flags)
> > +{
> > +	return NULL;
> > +}
> > +#endif
> 
> This would move a new conditionally compiled ".c" file for just these
> trace helpers.
> 
> >  struct json_object *util_cxl_memdev_to_json(struct cxl_memdev *memdev,
> >  		unsigned long flags)
> > diff --git a/cxl/list.c b/cxl/list.c
> > index 0b25d78248d5..48bd1ebc3c0e 100644
> > --- a/cxl/list.c
> > +++ b/cxl/list.c
> > @@ -146,6 +146,12 @@ int cmd_list(int argc, const char **argv, struct cxl_ctx *ctx)
> >  		param.ctx.log_priority = LOG_DEBUG;
> >  	}
> >  
> > +#ifndef ENABLE_LIBTRACEFS
> > +	if (param.media_errors) {
> > +		notice(&param, "--media-errors support disabled at build time\n");
> > +		param.media_errors = false;
> > +	}
> > +#endif
> 
> This would be a static inline helper in a header file that optionally
> reports the problem.
> 
> All that said, I am not the maintainer so go with what you want, but
> leaking ifdef in ".c" is, in my opinion, a slow walk into an
> increasingly unreadable code base.

I can do what you suggest, with bells on!
See you in v3 :)